Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry.
Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like.
The art has looked towards azeotrope or azeotrope-like compositions including the desired fluorocarbon components such as trichlorotrifluoroethane which include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic or azeotrope-like compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e., is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotrope-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity.
The art is continually seeking new fluorocarbon based azeotrope-like mixtures which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Currently, of particular interest, are fluorocarbon based azeotrope-like mixtures which are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, such as 1,1-dichloro-1-fluoroethane (HCFC-141b) and dichlorotrifluoroethane (HCFC-123 or HCFC-123a), will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to the fully halogenated species. Both HCFC-141b and dichlorotrifluoroethane are known to be useful as solvents. HCFC-141b has a boiling point of about 32.degree. C. HCFC-123 has a boiling point of about 27.8.degree. C. while HCFC-123a has a boiling point of about 29.9.degree. C.
The use of the aerosol packaging concept has long been found to be a convenient and cost effective means of dispensing solvents. Aerosol products utilize a propellant gas or mixture of propellant gases, preferably in a liquified gas rather than a compressed gas state, to generate sufficient pressure to expel the active ingredients, i.e. product concentrates such as solvents, from the container upon opening of the aerosol valve. The propellants may be in direct contact with the solvent, as in most conventional aerosol systems, or may be isolated from the solvent, as in barrier-type aerosol systems.
The art is also seeking new fluorocarbon azeotrope-like mixtures which are useful as blowing agents. Fluorocarbons such as trichlorofluoromethane have been used commercially as auxiliary blowing agents for flexible foams and as primary blowing agents for rigid foams. Polyurethane foams are manufactured by reacting and foaming a mixture of ingredients comprising in general an organic isocyanate, such as pure or crude toluene diisocyanate or a polymeric diisocyanate, with an appropriate amount of polyol or mixture of polyols, in the presence of a volatile liquid blowing agent, which vaporizes during the reaction, causing the polymerizing mixture to foam. The reactivity of these ingredients is enhanced through the use of various additives such as amine and/or tin catalysts and surfactant materials which serve to control and adjust cell size as well as to stabilize the foam structure during its formation.
Flexible polyurethane foams are generally manufactured using an excess of diisocyanate which reacts with the water also included as a raw material, producing gaseous carbon dioxide, causing foam expansion. Flexible foams are widely used as cushioning materials in items such as furniture, bedding and automobiles. Auxiliary physical blowing agents such as methylene chloride and/or CFC-11 are required in addition to the water/diisocyanate blowing mechanism in order to produce low density, soft grades of flexible polyurethane foam.
Rigid polyurethane foams are almost exclusively expanded using CFC-11 as the blowing agent. Some rigid foam formulations do incorporate small amounts of water in addition to the CFC-11, but the CFC-11 is the major blowing agent component. Other formulations sometimes use small amounts of the more volatile dichlorodifluoromethane (CFC-12) in addition to CFC-11 for producing so-called froth-type foams. Rigid foams are closed-cell foams in which the CFC-11 vapor is trapped in the matrix of cells. These foams offer excellent thermal insulation characteristics, due in part to the low vapor thermal conductivity of CFC-11, and are used widely in thermal insulation applications such as roofing systems, building panels, refrigerators and freezers and the like.
Commonly assigned U.S. Pat. No. 4,836,947 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane and ethanol. Commonly assigned U.S. Pat. NO. 4,842,764 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane and methanol. Commonly assigned U.S. Pat. No. 4,863,630 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and ethanol. Commonly assigned U.S. Pat. No. 4,894,176 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and methanol.
Kokai Patent Publication 103,686, published Apr. 20, 1989, discloses an azeotropic mixture of 55 to 80 weight percent dichlorotrifluoroethane and 20 to 45 weight percent 1,1-dichloro-1-fluoroethane. Kokai Patent Publication 136,981, published May 30, 1989, discloses a degreasing cleaning agent of 25 weight percent n-heptane and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 50 weight percent 1,1-dichloro-2,2,2-trifluoroethane.
Kokai Patent Publication 136,982, published May 30, 1989, discloses a buff-grinding cleaning agent of 25 weight percent n-hexane and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 50 weight percent 1,1-dichloro-2,2,2-trifluoroethane. Kokai Patent Publication 137,253, published May 30, 1989, discloses a resist developing agent of 25 weight percent n-heptane and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 50 weight percent 1,1-dichloro-2,2,2-trifluoroethane.
Kokai Patent Publication 137,259, published May 30, 1989, discloses a resist separating agent of 15 weight percent n-pentane, 10 weight percent alkyl benzene sulfonic acid, and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 50 weight percent 1,1-dichloro-2,2,2-trifluoroethane. Kokai Patent Publication 138,300, published May 31, 1989, discloses a flux cleaning agent of 25 weight percent n-heptane and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 50 weight percent 1,1-dichloro-2,2,2-trifluoroethane.
Kokai Patent Publication 139,104, published May 31, 1989, discloses a solvent of 5 weight percent n-heptane, 20 weight percent methanol, and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 75 weight percent 1,1-dichloro-2,2,2-trifluoroethane. Kokai Patent Publication 139,861, published June 1, 1989, discloses a dry-cleaning agent of 25 weight percent n-heptane and 75 weight percent of an azeotropic composition of 25 weight percent 1,1-dichloro-1-fluoroethane and 75 weight percent 1,1-dichloro-2,2,2-trifluoroethane.
It is an object of this invention to provide novel azeotrope-like compositions based on HCFC-141b and dichlorotrifluoroethane which are liquid at room temperature, which will not fractionate substantially under the process of distillation or evaporation, and which are useful as solvents for use in vapor degreasing and other solvent cleaning applications including defluxing applications and dry cleaning and as blowing agents for the preparation of polyurethane and polyisocyanurate foams.
Another object of the invention is to provide novel environmentally acceptable solvents for use in the aforementioned applications.
A further object of the invention is to provide novel environmentally acceptable blowing agents for the production of rigid and flexible polyurethane and polyisocyanurate foams.
Other objects and advantages of the invention will become apparent from the following description.